1. Field of the Invention
The present invention relates to a drilling head attached to a leading end of a rotary shaft, capable of reducing drilling resistance and easily drilling the ground to put the rotary shaft into the ground. The present invention also relates to a method of and an apparatus for soil improvement work with the use of the drilling head.
2. Description of the Related Art
A method of soil improvement work generally includes feeding a fluid from a fluid source on the ground to a leading end of a rotary shaft to be penetrated into the ground and ejecting the fluid from an ejection mouth toward the ground to be drilled, the ejection mouth being arranged on a mixing blade or a drilling head attached to the leading end of the rotary shaft.
Related arts are disclosed in, for example, Japanese Unexamined Patent Application Publications No. 2002-13131 and No. 2002-74049. According to the related arts, supply sources installed on the ground feed compressed air and a liquid through separate paths formed inside a rotary shaft to a leading end of the rotary shaft and eject the liquid with the compressed air from a mixing ejector arranged on a mixing blade toward drilled soil.
FIG. 1 shows an apparatus for soil improvement work disclosed in the Japanese Unexamined Patent Application Publication No. 2002-13131. In FIG. 1, a rotary shaft 501 is penetrated into the ground. The rotary shaft 501 incorporates an air path 502 for passing compressed air and a liquid path 503 for passing a liquid material. The air path 502 has a top inlet 502a that is connected to piping 504a extending from an air source 504 for supplying compressed air. The liquid path 503 has a top inlet 503a that is connected to piping 505a extending from a liquid source 505 for supplying the liquid material.
The air path 502 has a bottom outlet 502b, and the liquid path 503 has a bottom outlet 503b. The outlets 502b and 503b are connected to a mixing ejector 507 arranged on a mixing blade 506 attached to a lower end of the rotary shaft 501. The mixing ejector 507 mixes the compressed air supplied through the air path 502 with the liquid material supplied through the liquid path 503 and ejects the mixture.
FIG. 2 shows an example of a drilling head according to a related art used for an apparatus for soil improvement work. This drilling head is disclosed in Japanese Unexamined Patent Application Publication No. 2005-133367. In FIG. 2, the drilling head 520 is attached to a leading end of a rotary shaft 501. The drilling head 520 has a convex shape with a downward apex being on an axis of rotation. Along each ridge slope of the drilling head 520, drill bits 522 are arranged.
FIG. 3 shows another example of a drilling head disclosed in Japanese Unexamined Patent Application Publication No. 2006-37708. In FIG. 3, the drilling head 620 is attached to a leading end of a rotary shaft 501. The drilling head 620 has two spiral blades 621. Bottom edges of the spiral blades 621 are in the same virtual plane and each of the bottom edges is provided with drill bits 622 whose tips are substantially at the same level.